JPH09265021A - Multifiber core, optical amplifier formed by using the same, optical amplifier repeater formed by using the optical amplifier and optical amplifier distributor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to attain a value at which the flatness of the wavelength characteristic of a gain is satisfied in a high gain region of about 40dB. SOLUTION: Cores 1a to 1f are arranged around a core 1g. The rare earth elements and Al are added together to the respective cores la to 1g and are respectively coated with primary clad layers 2 having the refractive index n The rods constituted in such a manner are bundled and are disposed in this state in the central part of a secondary clad layer 3 having the refractive index nc (nc >np ). The core 1g has the refractive index 1% and the cores 1a to 1f have the refractive index nWO. Both are in the relation nWO>nWC. The power propagating in the core 1g is lowered by this constitution and the power balance with the other cores 1a to 1f is obtd. The flatness of the wavelengths is eventually improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-core fiber which is required to have a flat gain wavelength characteristic, an optical amplifier using the same, an optical amplification repeater and an optical amplification / distribution device using the optical amplifier. is there.

[0002]

2. Description of the Related Art In recent years, optical fiber amplifiers in which a rare earth element such as Er (erbium), Pr (praseodymium), or Nd (neodymium) is added to the core of an optical fiber have reached a practical level. In particular, an Er-doped optical fiber amplifier has a high gain and a high saturation output in the 1.55 μm band, and is therefore expected to be applied to various systems. Among them, 1.53μm to 1.56μ
High-speed, large-capacity, long-distance transmission and optical CATV (Cable Televis) by wavelength multiplex transmission using several or more wavelengths of signal light in m wavelength band
Ion) application to the system is attracting attention. When the Er-doped optical fiber amplifier is applied to such a system, the gain of the Er-doped optical fiber amplifier in the above-mentioned wavelength band is flat in order to suppress the deterioration of the optical S / N characteristic and the crosstalk characteristic. This is very important.

In order to achieve such high gain and flattening, the present inventors have previously shown the Er-doped multicore fiber as shown in FIG. 16 and the Er-doped multicore fiber as shown in FIG. I am proposing an optical amplifier. First, the Er-doped multi-core fiber 37 used
Is the primary clad layer 32, as shown in FIG.
A plurality of glass rods 34 (7 in the figure) provided with cores 31 _{-1 to} 31 _-7 in which a rare earth element (Er, for example, Er) and Al (aluminum) are co-added are assembled, and further, these glass The structure is such that the circumference of the rod 34 is covered with the clad 33. By using such an optical fiber, it is possible to achieve a high gain and a flat gain wavelength characteristic.

There are two reasons for this achievement. First, the first reason is that the Er-doped multi-core fiber can have a sufficiently high Al-doped concentration relative to a conventional Er-doped fiber having one core. The second reason is that when the power of the pumping light in the core is lowered with the conventional optical fiber, the gain peak near the wavelength of 1.535 μm decreases, and the gain-wavelength characteristic gradually becomes flat. Wavelength 1.53 as power is further reduced
Since the gain in the short wavelength region on the μm side is reduced and the gain in the long wavelength region on the 1.56 μm side is increased, that is, gain-wavelength characteristics that rise to the right from the short wavelength to the long wavelength, the pumping light is lowered. It has been known that the gain becomes extremely low and it cannot be used as an optical amplifier as it goes, but this Er-doped multi-core fiber, on the contrary, actively uses this principle. That is, as shown in the figure, the core diameter D and the core interval d should be optimized so that the pumping light and the signal light propagate almost uniformly in the Er-doped cores 31 _{-1 to} 31 _-7 . For example, although the amplification gain of the signal light propagating inside each of the cores 31 _{-1 to} 31 _-7 becomes low, its wavelength characteristic becomes almost flat, and after propagating a desired length, Uses that the signals amplified in each of the cores 31 _{-1 to} 31 _-7 are superposed, and the wavelength characteristic of the gain is almost flat.

Next, the configuration of the optical amplifier of FIG. 17 based on the above-mentioned principle and the result of evaluation of the wavelength characteristic of gain with respect to it will be described. Er-doped multi-core fiber 3
7, the core spacing d is 1.3 μm, and each core diameter is about 2 μm.
m, the clad diameter is 125 μm, the relative refractive index difference Δ between the core and the clad is 1.45%, and the mode field diameter is about 8.8.
μm, the addition amount of Er and Al in each core is 400 pp
m and 8500 ppm, and the fiber length was about 45 m. Isolators 35a and 35b for preventing light from propagating in the opposite directions are connected to both ends of the Er-doped multi-core fiber 37, and WDM is provided inside each of them.
(Wavelength Division Multiplexing)
Couplers 36a and 36b are provided. The signal light S ₁ is input to the isolator 35a, and the isolator 35b
The amplified signal light S ₂ is output from the.

Optical fibers 39a and 39b connected to pumping semiconductor lasers 38a and 38b are coupled to the WDM couplers 36a and 36b, respectively, and pumping lights 40a and 40b generated by the pumping semiconductor lasers 38a and 38b. Can be propagated to the Er-doped multi-core fiber 37. The signal light S passes through the isolator 35a.
_{When 1} is incident, a laser beam having a short wavelength is generated by the pumping semiconductor laser 38a, and this laser beam is incident on the Er-doped multicore fiber 37 via the WDM coupler 36a. Are excited and an amplification effect due to stimulated emission occurs. The amplified optical signal S ₂ is output from the Er-doped multicore fiber 37 to the outside through the isolator 35b. Similarly, the laser light generated by the pumping semiconductor laser 38b is incident on the Er-doped multicore fiber 37 from the rear direction,
Optical amplification is performed according to the principle described above. Here, the excitation light is applied from the front and back, but it may be applied either before or after.

Here, the wavelengths of the pumping lights 40a and 40b are set to 0.98 μm, and the pumping light power of the pumping light 40a is 70
The excitation light power of the excitation light 40b was set to 80 mW. These values are values determined from the fact that the gain wavelength characteristic is suitable for flattening. FIG. 18 shows the wavelength characteristic of gain in the configuration of FIG. That is, the signal light power Sp is -37 dB, -27 dB,-.
It is the result of measuring the wavelength characteristics of the respective gains in the cases of 17 dB and -9 dB. As is clear from FIG. 18, the gain is flattened over a wide wavelength range.

FIG. 19 shows an Er-doped multicore fiber 37.
18 is an experimentally obtained plot of the relationship between the core spacing d and the bandwidth when the gain is reduced by 1 dB from the maximum value (hereinafter referred to as “1 dB bandwidth”). The optical power Sp is used as a parameter. When the core interval d is 0, it is a characteristic of the conventional Er-doped optical fiber amplifier (so-called one having a single core structure). FIG.
As is clear from the above, it is shown that the Er-doped multicore fiber amplifier has a flatter gain wavelength characteristic, and that the 1 dB bandwidth is widened as the core spacing d is increased.

[0009]

However, according to the conventional Er-doped multi-core fiber amplifier, although a flat wavelength characteristic can be obtained when the gain is below a certain level, it is 40 dB.
In the front and rear high gain regions, satisfactory wavelength wavelength characteristics of gain were not obtained. Therefore, the present invention is a multi-core fiber that can obtain sufficient flatness characteristics even at high gain,
An object of the present invention is to provide an optical amplifier using the same, an optical amplification repeater and an optical amplification distribution device using the optical amplifier.

[0010]

In order to achieve the above object, the present invention is a multi-core fiber constructed by coating a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index. In the first core, the plurality of cores are arranged in the central portion, have a first refractive index higher than the predetermined refractive index, and are arranged outside the first core, and the first core The second core has a second refractive index higher than the refractive index.

According to this structure, by making the refractive index of the first core smaller than that of the second core, the power propagating in the first core decreases, and the power in the first core and the second core decreases. The power propagating in the core becomes equal and the power imbalance disappears. As a result, the flatness of the gain wavelength characteristic can be improved. Al is added to the first and second cores in addition to the rare earth element, and the cladding layer is provided outside the primary cladding layer and the primary cladding layer that covers the first and second cores. It can be composed of a secondary cladding layer.

According to this structure, in addition to the rare earth element, A
By adding l, the absorption and scattering loss can be minimized, and the refractive index can be adjusted by Al. Further, by dividing the primary clad layer into the secondary clad layer, the relative refractive index difference Δ can be increased, and an optical fiber for optical amplifier with high efficiency (= high gain) can be obtained.

The primary cladding layer can have a smaller refractive index than the secondary cladding layer. With this configuration, it is possible to obtain an optical fiber for an optical amplifier with high efficiency (= high gain), which is suitable for manufacturing an optical fiber in which the refractive index of the primary cladding layer and the refractive index of the secondary cladding layer are different. it can.

The first and second cores are made of SiO.
₂ type glass, SiO ₂ —GeO ₂ type glass, or S
At least 5000 ppm of Al and at least 200 ppm of Er in the iO ₂ —GeO ₂ —P ₂ O ₅ based glass.
The composition can be added. According to this configuration,
When a rare earth element and Al are added together, absorption and scattering loss can be minimized, but the refractive index can be adjusted by Al.
You can only do it. However, SiO ₂ is replaced by GeO ₂ or P
By adding ₂ O ₅ , the relative refractive index difference Δ can be increased, and an optical fiber for optical amplifier with high efficiency (= high gain) can be obtained.

The above-mentioned object is a multi-core fiber constructed by coating a plurality of cores doped with a rare earth element with a cladding layer, wherein the plurality of cores are arranged at the center of the first cores. And a second fiber which is arranged outside the first core and which includes a second rare earth element in an amount larger than the amount of the rare earth element added to the first core.

According to this structure, the amount of the rare earth element added to the first core is made smaller than that of the second core, so that the signal light power propagating through the first core, the pumping light power, and The amplification degree determined by the Er addition amount and the amplification degree determined by the signal light power propagating in the surrounding second core, the excitation light power and the Er addition amount can be made substantially equal. As a result, the wavelength characteristic of gain can be flattened.

It is desirable that the first and second cores be added so that the rare earth element is distributed in the radial direction. According to this structure, the rare earth element is added to the shape close to the distribution of the signal light power and the pumping light power propagating in each core, and a high gain can be obtained. The first core may be configured to have a refractive index higher than that of the cladding layer and lower than that of the second core.

According to this structure, in addition to the effect of adjusting the amount of Er added, the power propagating in the first core is reduced by making the refractive index of the first core smaller than that of the second core. The power is reduced and the powers propagating in the first core and the second core become equal, and the power imbalance disappears. As a result, the flatness of the gain wavelength characteristic can be improved. Al is added to the first and second cores in addition to the rare earth element, and the cladding layer is provided outside the primary cladding layer and the primary cladding layer that covers the first and second cores. It can be composed of a secondary cladding layer.

According to this structure, in addition to the rare earth element, A
By adding l, the absorption and scattering loss can be minimized, and the refractive index can be adjusted by Al. Further, by dividing the primary clad layer into the secondary clad layer, the relative refractive index difference Δ can be increased, and an optical fiber for optical amplifier with high efficiency (= high gain) can be obtained. The primary clad layer may have a refractive index smaller than that of the secondary clad layer.

According to this structure, it is suitable to manufacture an optical fiber in which the refractive index of the primary cladding layer and the refractive index of the secondary cladding layer are different, and high efficiency (= high gain) is obtained.
The optical fiber for the optical amplifier can be obtained. The first and second cores are made of SiO ₂ glass, SiO ₂ -G.
eO ₂ based glass or SiO ₂ -GeO ₂ -P ₂ O,
Al at least 5000ppm in ₅ series glass, and E
It can be configured such that r is at least 200 ppm.

According to this structure, when the rare earth element and Al are added together, the absorption and scattering loss can be minimized, but the refractive index can be adjusted only by Al. However, by adding GeO ₂ or P ₂ O ₅ to SiO ₂ , the relative refractive index difference Δ can be increased, and a high efficiency (= high gain) optical amplifier optical fiber can be obtained. Further, the above-mentioned object of the present invention is constituted by coating a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index, wherein the plurality of cores are arranged at the center and A first core having a first index of refraction greater than the first index of refraction, and a second core disposed outside the first core and having a second index of refraction greater than the first index of refraction. And a W provided on the input side, output side, or both sides of the multicore fiber.
Achieved by an optical amplifier using a multi-core fiber having a DM circuit, a pumping light source for supplying pumping light to the WDM circuit, and an isolator provided between the WDM circuit and an input end or an output end. To be done.

According to this structure, the rare earth-doped multi-core fiber in consideration of the refractive index of the core is excellent in the flat characteristic of the gain wavelength characteristic, and by combining this with the WDM circuit, the pumping laser light is converted into the rare earth-doped multi-core fiber. It can be injected, which allows optical amplification to occur. As a result, it is possible to increase the gain while ensuring the flat characteristic of the gain wavelength characteristic. Furthermore, the above-mentioned purpose is
A plurality of cores to which a rare earth element is added are covered with a clad layer having a predetermined refractive index, and the plurality of cores include a first core arranged at the center of the plurality of cores, and A multi-core fiber, which is arranged outside the first core and includes a second core containing a rare earth element in an amount larger than the amount of the rare earth element added to the first core, and an input side and an output side of the multi-core fiber. , Or a WDM circuit provided on both sides, a pumping light source for supplying pumping light to the WDM circuit, and an isolator provided between the WDM circuit and an input end or an output end. It is also achieved by an optical amplifier.

According to this structure, the rare earth-doped multi-core fiber in which the amount of the rare earth element added to the second core is larger than that of the first core is excellent in the flat characteristic of the gain wavelength characteristic, and by combining this with the WDM circuit, Laser light for excitation can be injected into the rare-earth-doped multicore fiber, and thereby optical amplification can be performed. As a result, it is possible to increase the gain while ensuring the flat characteristic of the gain wavelength characteristic. The pumping light in the optical amplifier is 0.98.
Wavelengths in the μm band or 1.48 μm band can be used.

According to this structure, the wavelength in the 0.98 μm band contributes to obtaining an amplifier having a lower noise figure and a flat gain wavelength characteristic, and the wavelength in the 1.48 μm band is highly reliable. It contributes to obtaining a high gain. Further, the above-mentioned object of the present invention is constituted by coating a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index,
The plurality of cores are disposed at a central portion, have a first refractive index higher than the predetermined refractive index, and the first core have a first refractive index higher than the predetermined refractive index, and the first core has a first refractive index. A multi-core fiber composed of a second core having a larger second refractive index, a WDM circuit provided on the input side, output side, or both sides of this multi-core fiber, and pumping light is supplied to this WDM circuit A pumping light source, an isolator provided between the WDM circuit and an input end or an output end, and a dispersion shift fiber connected to the input side, the output side, or both sides of the optical amplifier of the multicore fiber. This is achieved by the optical amplification repeater having the configuration provided.

According to this structure, the mode field diameters of the dispersion-shifted fiber and the rare-earth-doped multicore fiber are very close to each other while the flatness of the wavelength characteristic of the gain is ensured and the gain is increased. It is possible to obtain an optical amplification repeater capable of transmitting the signal with low connection loss. Further, the above-mentioned object is constituted by coating a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index, and the plurality of cores are arranged at the center of the plurality of cores. A multi-core fiber comprising a first core and a second core which is arranged outside the first core and which contains a rare earth element in an amount larger than the rare earth element addition amount of the first core; A WDM circuit provided on the input side, output side, or both sides of the fiber, and a pumping light source for supplying pumping light to this WDM circuit,
An optical amplification repeater having a configuration including an isolator provided between the WDM circuit and an input end or an output end, and a dispersion shift fiber connected to an input side, an output side, or both sides of the multicore fiber optical amplifier. Achieved by

According to this structure, the mode field diameters of the dispersion-shifted fiber and the rare earth-doped multi-core fiber are very close to each other while the flatness of the wavelength characteristic of the gain is ensured and the gain is increased. It is possible to obtain an optical amplification repeater capable of transmitting the signal with low connection loss. Furthermore, in the optical amplification repeater, a dispersion compensation device may be connected in the middle of the dispersion shift fiber.

With this configuration, the dispersion compensating device compensates the dispersion value of the fiber, which is a problem when transmitting high-speed, large-capacity information over a longer distance.
Therefore, a large amount of information can be transmitted at a high speed to a distant place while ensuring the flatness of the gain wavelength characteristic and the high gain. Further, in the optical amplification repeater, an optical multiplexing / demultiplexing circuit can be provided on the input side, output side, or both sides.

According to this configuration, wavelength multiplexing can be performed by the optical multiplexing / demultiplexing circuit, and long-distance transmission can be performed by passing the wavelength-multiplexed signal light through the rare earth-doped multicore fiber and the dispersion shift fiber. Further, the above-mentioned object of the present invention is constituted by coating a plurality of cores to which a rare earth element is added with a cladding layer having a predetermined refractive index, wherein the plurality of cores are arranged at the center and A first core having a first index of refraction greater than the index of refraction of
A multi-core fiber, which is arranged outside the first core and includes a second core having a second refractive index higher than the first refractive index, and an input side, an output side of the multi-core fiber, or WDM circuits provided on both sides, and a pumping light source for supplying pumping light to the WDM circuits,
An optical amplifier provided with an isolator provided between the WDM circuit and an input end or an output end, and an optical signal after amplification provided on the output side of the optical amplifier and output from the optical amplifier are different from each other. This can also be achieved by a multi-core fiber optical amplification / distributing device having a configuration provided with an optical star coupler that distributes and outputs wavelengths.

According to this structure, the optical signal is amplified by the optical star coupler while the flatness of the gain wavelength characteristic is ensured by the optical amplification using the rare earth-doped multi-core fiber, and the wavelength multiplexing is performed to the plurality of subscribers. The converted information signal can be transmitted almost evenly, and the S / N deterioration and the crosstalk characteristic deterioration can be made extremely low. Further, the above-mentioned object of the present invention is constituted by coating a plurality of cores to which a rare earth element is added with a clad layer having a predetermined refractive index, and the plurality of cores are provided at the center of the plurality of cores. A multi-core fiber composed of a first core arranged and a second core arranged outside the first core and containing a rare earth element in an amount larger than the rare earth element addition amount of the first core; , A WDM circuit provided on the input side, output side, or both sides of this multi-core fiber,
A pumping light source for supplying pumping light to the WDM circuit, an optical amplifier including an isolator provided between the WDM circuit and an input end or an output end, and an output side of the optical amplifier, This can also be achieved by an optical amplification / distribution device having a configuration including an optical star coupler that distributes and outputs the amplified optical signal output from the optical amplifier to a plurality of different wavelengths.

According to this structure, the signal light amplified by optical amplification using the rare earth-doped multi-core fiber while ensuring the flatness of the gain wavelength characteristic is distributed by the optical star coupler, and wavelength-division multiplexed to a plurality of subscribers. The converted information signal can be transmitted almost evenly, and the S / N deterioration and the crosstalk characteristic deterioration can be made extremely low.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of an Er-doped multicore fiber according to the present invention, (a) is a sectional view, (b) is AA ′, BB ′ in (a),
The refractive index distribution in each cross section of CC 'is shown.

Before describing the structure of the multicore fiber according to the present invention, the background of the invention of the multicore fiber having the structure according to the present invention will be described. When theoretically analyzing the power distribution in each core in a state of propagating 1 m in the Er-doped multicore fiber when pumping light having a wavelength of 0.98 μm and signal light having a wavelength of 1.55 μm are incident on the Er-doped multicore fiber, FIG. 14 (in the figure, (a) is a cross-sectional view of the fiber, (b) is a wavelength of 0.98μ
(Indicates core spacing d-power incidence / emission characteristics at m)
And the result of FIG. 15 (showing the core interval d-power entrance / exit characteristics at a wavelength of 1.55 μm) was obtained. In each case, the relationship between the power ratio and the core spacing is shown. The horizontal axis shows the spacing d between the cores, and the vertical axis shows the ratio of the power input to and output from each core.

According to the theoretical analysis by the inventors, the AA axis, the BB axis, and the C-axis in FIGS.
Since the C axis is symmetrical, the power ratios of the peripheral portions are equal. Therefore, in FIGS. 14 and 15, the minimum value and the maximum value of the power ratio in the core in the central portion and the power ratio in the core in the peripheral portion are plotted. First, FIG.
In the case of No. 4, when the core spacing d is small with respect to the excitation light having a wavelength of 0.98 μm, there is a large difference between the minimum value and the maximum value of the power ratio of the central portion and the peripheral portion. That is, the pumping light propagates in each core with a large vibration, and a large power imbalance occurs between the power in the central core and the power in the peripheral cores. However, when the core spacing d is gradually increased, the power imbalance becomes smaller, and the powers in the cores at the central portion and the peripheral portion become close to each other in the range of the core spacing d of 1.3 to 1.5 μm. It turned out to be.

FIG. 15 also shows the same tendency with respect to the signal light having a wavelength of 1.55 μm, and the core spacing d for propagating the pumping light and the signal light in the respective cores is almost evenly distributed. It was found that the optimum value was in the range of 1.3 to 1.5 μm. However, as can be seen from the above results, there is still an imbalance in the power propagating in the central core and the peripheral core, and as shown in FIG. 18, the flatness of the gain wavelength characteristic is deteriorated. It is thought to be the cause of this.

Therefore, in the present invention, FIG. 14 and FIG.
In Fig. 5, the refractive index (n _WC ) of the central core is lower than the refractive index (n _wo ) of the cores arranged around the central core so that the powers propagated in the central core and the peripheral core become more equal. The value is set so that the power propagating in the core at the center is reduced. As a result, the power propagating in the core of the central portion and the power propagating in the core of the peripheral portion can be made substantially equal, and the flatness of the gain wavelength characteristic can be improved.

Next, an embodiment of the present invention embodying the above idea will be described with reference to FIG. Core 1
a to 1 g are covered with the primary cladding layer 2. Er and Al are co-added to the cores 1a to 1g. And one core 1a to 1g (core 1g = first
6) (core 1) is placed at the center, and the other 6 cores (core 1a to 1f = second core) are integrally bundled so as to surround the core. These cores 1a to 1g are further covered with a secondary clad layer 3. When the refractive index of the secondary clad layer 3 is n _C , the cores 1a to 1f have different refractive indices n _WO , and the central core 1g has a refractive index n _WC . That is, with respect to the refractive index n _C of the secondary clad layer 3, the refractive index n _{WO of the} cores 1a to 1g.
Is set so that n _WO > n _C, and the refractive index n _WO of the cores 1a to 1g is n _WC <for the refractive index n _WC of the core 1g.
n _WO . The refractive index n _P of the primary cladding layer 2 is set to n _C = n _P with respect to the refractive index n _C of the secondary cladding layer 3.

FIG. 1 (b) shows A- in FIG. 1 (a).
The refractive index distribution in each cross section of A ', BB', and CC 'is shown. The refractive index n _WC of the central core 1g is set to be lower than the refractive index n _WO of the surrounding cores 1a to 1g, and the signal light (wavelength 1.53) propagating through the central core 1g.
.About.1.57 .mu.m band) and the excitation light (0.98 .mu.m band or 1.48 .mu.m band) power amount is suppressed as compared with the value in the case of FIG. Since even distribution can be achieved, the wavelength characteristic of gain can be further flattened.

The core material of the Er-doped multi-core fiber having the structure shown in FIG. 1 is SiO ₂ --GeO ₂ --Al ₂
Er is added to O ₃ . The primary clad layer 2 and the secondary clad layer 3 are made of SiO ₂ . As a specific example, the outer diameter of the secondary clad layer 3 is 125 μm, the core outer diameter of the cores 1a to 1g is about 1.9 μm, and the core interval of the cores 1a to 1g is about 1.3 μm.
m, refractive index n _WC of central core 1 g is 1.478, core 1
a to 1f has a refractive index n _WO of 1.4795, the primary cladding layer 2 has a refractive index n _P and the secondary cladding layer 3 has a refractive index n _C of 1.458, and Er and A in the cores 1a to 1g.
The addition amount of 1 was 400 ppm and 8,500 ppm, respectively. The distance between the cores 1a to 1g of about 1.3 μm was controlled by the thickness of the primary cladding layer 2.

Then, the gain characteristic and the 1 dB bandwidth characteristic were measured by the configuration shown in FIG. As a result, the results shown in FIGS. 2 and 3 were obtained. 2 and 3
As is clear from, small signal input (Sp = -37 dB
The wavelength characteristic of gain in the case of m) is flattened. That is, in the past, the 1 dB bandwidth (the bandwidth in which the gain is reduced by 1 dB) was about 15 nm, but according to the present invention, it is about 2 dB.
It was possible to expand to 2 nm. Also, cores 1a to 1g
When the amount of Al added therein was 17,000 ppm, the 1 dB bandwidth when the small signal was input could be expanded to about 26 nm.

FIG. 4 shows a second embodiment of the Er-doped multicore fiber according to the present invention, (a) is a sectional view,
(B) is A-A ', BB', C in (a) of FIG.
The refractive index distribution in each cross section of -C 'is shown. FIG.
In this configuration, the refractive index n _C of the secondary clad layer 3 with respect to the refractive index n _P of the primary clad layer 2 is n _C = n _P
In contrast to this, in this configuration, the refractive index n _P of the primary cladding layer 2 and the refractive index n _C of the secondary cladding layer 3 in FIG. 1 are set to different values (n _C > n _P ). For example, when the refractive index n _C of the secondary cladding layer 3 is set to 1.458, the refractive index n _P of the primary cladding layer 2 is set to 1.448 by adding fluorine. According to this setting, the relative refractive index difference Δ _O between the refractive index n _WO of the cores 1a to 1f and the refractive index n _P of the primary cladding layer 2 is 2.15%, the refractive index n _WC of the core 1g and the primary cladding layer 2 are The relative refractive index difference Δ _C of the refractive index n _P is set to 2.03%, and the relative refractive index difference can be made larger than that of the fiber of FIG. As a result, the confinement of the signal light and the pumping light in the core can be strengthened. As a result, the gain can be increased by about 2 dB as compared with the configuration of FIG. 1, and the 1 dB bandwidth can be obtained to a value similar to that of the fiber of the configuration of FIG.

The core material of the Er-doped multicore fiber having the structure shown in FIG. 4 is SiO ₂ --GeO ₂ --Al ₂
Er is added to O ₃ . Further, as the primary clad layer 2, SiO ₂ with F added is used,
SiO ₂ is used for the secondary cladding layer 3. 5A and 5B show a third embodiment of an Er-doped multicore fiber according to the present invention, wherein FIG. 5A is a sectional view and FIG. 5B is AA ', BB', C- in FIG. 5A. The refractive index distribution in each cross section of C'is shown.

In FIGS. 1 and 4, SiO ₂ --GeO is used.
The structure of the Er-doped multi-core fiber having _2- Al ₂ O ₃ as the main material of the core has been described.
The structure of the Er-doped multi-core fiber having _2- Al ₂ O ₃ as the main material of the core will be described. Central core 1g
Is composed of a material obtained by adding Er to SiO ₂ —Al ₂ O ₃ . The amount of Al ₂ O ₃ was added as much as 5 to 6% (60,000 ppm at maximum). Core 1a
In order to make the refractive index larger than that of the central core 1g, SiO ₂ -Al ₂ O ₃ with Er added (about the same amount of Al ₂ O ₃ as the central core 1g) is used for adjusting the refractive index. As a material, a small amount of GeO ₂ or P ₂ O ₅ is added. Even in the central core 1g, P ₂ O
₅ may be added. Since the upper limit of the feasible refractive index of SiO ₂ —Al ₂ O ₃ glass is about 1.478, the relative refractive index difference Δ cannot be made too large. When it is desired to increase the relative refractive index difference Δ, the primary cladding layer 2 may be formed by using SiO ₂ containing fluorine as described with reference to FIG. 6, and the refractive index of the primary cladding layer 2 may be lowered.

The feature of the multi-core fiber having the configuration of FIG. 5 is that Al ₂ O ₃ is added to each core as much as possible, and GeO ₂ or P ₂ O is added to the surrounding cores 1a to 1f.
By adding ₅ and making the refractive index larger than that of the central core 1g, it is possible to realize flattening of the gain wavelength characteristic over a wider band. In addition, by adding P ₂ O ₅ to each core, it is possible to have an auxiliary role for adding Er in a more uniform and more uniform manner. It is also effective for flattening the wavelength characteristics.

FIG. 6 shows a fourth embodiment of an Er-doped multicore fiber according to the present invention, (a) is a sectional view,
(B) is A-A ', BB', and C in (a) of FIG.
The refractive index distribution in each cross section of -C 'is shown. FIG.
In the multi-core fiber of FIG. 1, cores 1a to 1g each having a primary clad layer 2 are integrated with the configuration of FIG. 1, and the periphery thereof is covered with an intermediate layer 100 in a cylindrical shape. It is configured to be covered with the secondary cladding layer 3. As the material of the intermediate layer 100, SiO ₂ with F added can be used, and its diameter is 10 to 1
A range of 00 μm is preferred.

According to the structure of FIG. 6, the same refractive index distribution as that of the structure of FIG. 4 can be provided, and the effect of confining each of the signal light and the pumping light in the core by increasing the relative refractive index difference. Can be higher. In the configurations of FIGS. 1, 4, 5, and 6, the refractive index distribution in the cores 1a to 1g is stepwise as shown in (b) of each figure, but is not limited to stepwise. However, it may have a gentle distribution in the radial direction. Further, the refractive indexes in the primary cladding layer 2 and the intermediate layer 100 may also have a distribution other than the stepwise distribution.

FIGS. 7 and 8 show an example of the Er-doped concentration distribution in each of the AA ', BB', and CC 'cross sections in FIGS. 1, 4, 5, and 6 (a). It is the figure which showed. As described above, the Er addition concentration in the cores 1a to 1f may also have a stepwise shape as shown in FIG. 7 or a gentle radial distribution as shown in FIG. The first to fourth embodiments described so far reduce the power propagating through the central core 1g by lowering the refractive index of the central core 1g lower than that of the surrounding cores 1a to 1f. , The gain wavelength characteristic is flattened over a wide band by making it approximately equal to the power propagating in the surrounding cores 1a to 1f, but as shown in FIG. 7 and FIG. The signal light power propagating in the central core 1g even if only the means for reducing the amount of Er added to the central core 1g to be smaller than the amount of Er added to the surrounding cores 1a to 1f,
The amplification degree determined by the excitation light power and the amount of Er added,
The wavelength characteristics of the gain can be flattened by making the signal light power propagating through the surrounding cores 1a to 1f and the pumping light power and the amplification degree determined by the added amount of Er substantially equal to each other.

Further, means for making the refractive index of the central core 1g lower than the refractive index of the peripheral cores 1a to 1f, and the amount of Er added to the central core 1g are the peripheral cores 1a to 1f. Means for constituting less than the amount of Er added to 1f may be combined, and if both are combined,
This is convenient for flattening the gain wavelength characteristic. That is, the refractive index of the central core 1g is made lower than the refractive index of the peripheral cores 1a to 1f to suppress the signal light power and the pumping light power propagating through the central core 1g, and
The amount of Er added to g is made smaller than the amount of Er added to the surrounding cores 1a to 1f to suppress the amplification degree a little, and as a result, amplification of the signal light power of each of the cores 1a to 1g is achieved. Uniformity can be achieved. By combining both means in this way, it is possible to provide more freedom in the design of the Er-doped multicore fiber.

For example, in order to obtain desired characteristics, various combinations of the degree of decrease in the refractive index of the central core 1g and the degree of decrease in the Er addition amount are conceivable, and when the degree of decrease in the refractive index is small. For this purpose, the degree of decrease of the Er addition amount may be increased, and when the degree of decrease of the refractive index is large, the reduction degree of the Er addition amount may be decreased.

FIG. 9 is a connection diagram showing a first embodiment of an optical amplifier using an Er-doped multicore fiber according to the present invention. Lenses 5a and 5b are provided at both ends of the Er-doped multicore fiber 4, and WDM circuits 6a and 6b are provided so as to face the lenses 5a and 5b, respectively. Further, the lenses 7a and 7b are arranged at angular positions symmetrical with respect to the lenses 5a and 5b with respect to the vertical line with respect to the WDM circuits 6a and 6b.
Are arranged. Further, lenses 9a and 9b are arranged outside the WDM circuits 6a and 6b via bulk-structured isolators 8a and 8b. The lenses 9a and 9b are disposed.
Facing the input side, the input side fiber 10a and the output side fiber 1
0b is provided. Further, optical fibers 11a and 11b are arranged facing the lenses 7a and 7b, and pumping semiconductor lasers 12a and 12b (generating pumping lights 13a and 13b) are provided at respective ends of the optical fibers 11a and 11b. Each is arranged. Then, the signal light S ₁ is input to the optical fiber 10a, and the amplified signal light S ₂ is output from the optical fiber 10b. Each lens is used for converting non-parallel light into parallel light.

Here, the WDM circuits 6a and 6b are composed of interference film filters in which low refractive index layers and high refractive index layers of SiO ₂ and TiO ₂ films are alternately formed on a glass substrate, and transmit the signal light. In addition, the circuit has a characteristic of reflecting the excitation light. The reason why the fiber type structure is not used for the isolators 8a and 8b and the WDM circuits 6a and 6b is as follows.
This is because the Er-doped multi-core fiber 4 has a large relative refractive index difference Δ, so that when a fiber type structure is used, a mode field matching circuit must be provided, and a loss due to this must be avoided.

The signal light S ₁ incident on the input side fiber 10a is sent to the Er-doped multi-core fiber 4 via the lens 9a, the isolator 8a and the WDM circuit 6a, and at the same time, the WDM coupler 6a pumps a semiconductor laser for excitation. 1
Excitation light 13a is applied from 2a. The excitation light 13a incident on the Er-doped multicore fiber 4 excites a certain energy level of the ions, and an amplification action by stimulated emission occurs. The optical signal S ₂ amplified here is sent from the Er-doped multicore fiber 4 to the output side fiber 10b via the lens 5b, the WDM circuit 6b, and the isolator 8b in order. Similarly, the pumping light 13b generated by the pumping semiconductor laser 12b is the Er-doped multicore fiber 4
Then, the light is incident from the rear direction, and the light is amplified by the above-described principle. Here, the excitation light is applied from both front and rear directions, but it may be applied from either the front side or the rear side.

Isolators 8a and 8b for preventing light from propagating in opposite directions are connected to both ends of the Er-doped multi-core fiber 4, and WD is provided inside each of them.
M couplers 6a and 6b are provided. Isolator 8
The signal light S ₁ is input to a, and the amplified signal light S ₂ is output from the isolator 8b. FIG. 10 shows a second optical amplifier using an Er-doped multicore fiber according to the present invention.
It is a connection diagram showing an embodiment of.

The optical amplifier shown in FIG. 10 has a W difference from the configuration shown in FIG.
It is characterized in that the DM couplers 6a and 6b and the isolators 8a and 8b are interchanged. The other configuration is as shown in FIG. 9, and thus the description is omitted. In this case, the isolator 8a needs to have a characteristic of transmitting the signal light and the pumping light in the right direction of the drawing. That is, a broadband isolator that allows not only the wavelength band of the signal light (1.53 to 1.56 μm) to pass but also the wavelength band of the pump light (0.98 μm band or 1.48 μm band) is used. .

As shown in FIG. 10, isolators 8a and 8b are provided.
Is provided in the latter stage of the WDM couplers 6a and 6b,
Not only the signal light reflected from the Er-doped multicore fiber 4 side but also the excitation light can be blocked, so that the operations of the signal light side light source and the excitation semiconductor laser 12a can be stably held. Further, the pumping light 13b from the pumping semiconductor laser 12b propagates in the Er-doped multi-core fiber 4, is reflected by the isolator 8a, and is again E.
Since it propagates in the r-doped multi-core fiber 4, the pumping light can be more efficiently contributed to amplification, and as a result, high gain can be achieved.

FIG. 11 is a connection diagram showing an example of the configuration of an optical amplification / distribution device constructed using the optical amplifier shown in FIG. An amplification / distribution device is configured by connecting an optical star coupler 14 to the optical amplifier shown in FIG. That is, by connecting the optical star coupler 14 to the output side fiber 10b of FIG. 8, it is possible to obtain a plurality of signal output lights 15 obtained by distributing the amplified optical signal.

The input to the optical star coupler 14 is N (N:
1, 2) whose output is M (M: ≧ 2) are used, and one of the inputs is connected to the output side fiber 10b. Here, N is “2” and M is “16”, but N may be 1, and M is “4”, “8”, “32”,
It can be "64" or the like. Further, the optical star coupler 14 may have either a fiber type structure or a waveguide type structure.

The mode field diameters of the output side fiber 10b and the input side fiber of the optical star coupler 14 are Er.
If the mode field diameter of the doped multi-core fiber is made substantially equal, the output light 15 amplified and distributed can be taken out from the output side of the optical star coupler 14 with lower loss and elimination of reflected light. FIG. 12 is a connection diagram showing a configuration example of an optical amplification repeater configured by using the optical amplifier shown in FIG.

As shown in FIG. 12, a plurality of dispersion-shifted fibers 16a, 16b, 16c having the same specifications are used,
The Er-doped multi-core fiber amplifiers 17a and 17b having the configuration shown in FIG. 9 are arranged between them. Further, the optical amplifier 1 is provided on the output side of the dispersion shift fiber 16c.
7c is provided. The output side 19a of the optical multiplexer / demultiplexer circuit 18a is connected to the input side of the dispersion shift fiber 16a, and the optical multiplexer / demultiplexer circuit 18b is connected to the output end of the optical amplifier 17c.
Input port 20b is connected. Further, the optical multiplexing and demultiplexing circuit 18a includes an input port 20a, the wavelength lambda ₁ to [lambda] ₈
Optical signal is input. Furthermore, the optical multiplexing and demultiplexing circuit 18b includes an output port 19b, the optical signals amplified wavelength lambda ₁ to [lambda] ₈ is output separately.

In the configuration of FIG. 12, wavelengths λ _{1 to} λ ₈
When the optical signal of 1 is input to the optical multiplexer / demultiplexer circuit 18a, the optical signal wavelength-multiplexed by the optical multiplexer / demultiplexer circuit 18a passes through the dispersion shift fibers 16a, 16b, 16c and the optical amplifier 17a,
It is sequentially supplied to 17b and 17c, and optical amplification is performed. Finally, each wavelength (wavelength λ
The signal light of _{1 to} λ ₈ ) is separated and output. At this time, the wavelength characteristics of the gain of the optical amplifiers 17a, 17b, and 17c when a small signal is input are flat over a wide band as described above, so that more information can be added to the optical signals of the respective wavelengths for longer distances. Can be transmitted to. Further, the S / N and optical crosstalk characteristics of each channel at the output port 19b can be maintained at high performance.

Further, the dispersion shift fibers 16a, 16
b, 16c and the optical amplifiers 17a, 17b, 17c have mode field diameters close to each other, so that low reflection,
A low loss optical transmission system can be constructed. That is, it is possible to transmit high-speed, large-capacity information over a long distance with a low noise figure. In FIG. 12, the wavelength multiplexing number is 8 channels, but the number is not limited to this. For example, “16”, “32”, “64”,
The number of channels such as "128" can be set. Further, although the number of dispersion shift fibers and the number of optical amplifiers are each three, they can be set arbitrarily.

FIG. 13 is a connection diagram showing another configuration example of the optical amplification repeater. The amplification repeater shown here has a configuration using a fiber-type or waveguide-type dispersion compensation device 21 in place of the optical amplifier 17c in the configuration of FIG. When transmitting a large amount of information at high speed over a long distance with the configuration of FIG. 12, the dispersion characteristic of the fiber becomes a problem.
In order to solve this problem, the dispersion compensation device 21 is provided.

In each of the above-mentioned embodiments, the cores 1a to 1g have been described with reference to the example in which Er is added.
Instead of this, Pr (praseodymium), Nd, Yb (ytterbium), Sm (samarium), Ce (cerium)
Rare earth elements such as can be used. Further, as the rare earth element, at least two kinds of the above can be added.

The main material of the cores 1a to 1g is SiO.
_{Use of 2} system (SiO ₂ with at least one additive for controlling refractive index such as Ge, P, Al, Ti, B, F) added, fluoride system, or multi-component system material You can Further, the primary cladding layer 2 and the secondary cladding layer 3 are made of SiO ₂ or the above-mentioned SiO _2.
It is possible to use any of _two- system materials, fluoride-based materials, and multi-component materials.

[0064]

As described above, the present invention includes the first core and the second core arranged near the first core, and the first core is smaller than the second core. By setting the refractive index, the power of each core can be balanced and the gain wavelength characteristic can be made flat over a wide band.

If the core and the second core are each covered with the primary cladding layer and the outer circumferences of these cores are covered with the secondary cladding layer, the refractive index n _P of the primary cladding layer and the secondary cladding layer It is suitable for manufacturing fibers having different refractive indexes n _C , and an optical fiber for an optical amplifier with high efficiency (= high gain) can be obtained.

Further, the first portion disposed in the center of the clad
The amount of rare earth element added to the core of is smaller than the amount of rare earth element added to the surrounding second core,
Amplification degree determined by signal light power propagating in the first core, pumping light power and Er addition amount, and amplification degree determined by signal light power propagating in the surrounding second core, pumping light power and Er addition amount And can be approximately equal. Therefore, the wavelength characteristic of gain can be flattened.

The present invention also provides a rare earth-doped multi-core fiber in which the flatness of gain wavelength characteristics is improved, and WD
Since the optical amplifier is configured in combination with the M circuit, it is possible to increase the gain while ensuring the flatness of the gain wavelength characteristic. Furthermore, when the rare earth element is added, the refractive index of the first core is made smaller than the refractive index of the second core, so that the signal light power and the pumping light propagating in each of the first core and the second core are excited. The amplification degree determined by the power and the rare earth element can be made substantially equal.

Further, according to the present invention, by adding a dispersion shift fiber to an optical amplifier using a rare earth-doped multicore fiber, the mode field diameters of the dispersion shift fiber and the rare earth-doped multicore fiber can be made very close to each other. Therefore, it becomes possible to perform transmission of information signals with low connection loss. Further, according to the present invention, wavelength dispersion can be performed by adding a dispersion shift fiber and an optical multiplexing / demultiplexing circuit, and if the wavelength-multiplexed signal light is passed through each fiber, the flatness of the wavelength characteristic of gain and high gain can be maintained. However, it is possible to obtain an optical amplification repeater capable of long-distance transmission.

Further, in the present invention, since the dispersion compensating device is connected to the dispersion shift fiber, the dispersion value of the fiber, which is a problem when transmitting high-speed, large-capacity information over a longer distance, It is compensated by the dispersion compensation device. Therefore, it is possible to obtain an optical amplification repeater capable of transmitting a large amount of information at a high speed to a distant place while ensuring the flatness of the gain wavelength characteristic and the high gain.

Further, according to the present invention, the optical amplifier using the rare earth-doped multi-core fiber is provided with the optical star coupler so that the amplified optical signal is distributed and output to a plurality of different wavelengths. The signal light amplified by the optical amplification while ensuring the flatness of the wavelength characteristic of the gain is distributed by the optical star coupler, and the information signals wavelength-multiplexed to the plurality of subscribers are almost evenly distributed and the S / N ratio is increased. It is possible to obtain an optical amplifying / distributing device capable of transmitting deterioration and deterioration of crosstalk characteristics at an extremely low value.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of a multicore fiber according to the present invention.

FIG. 2 is a wavelength-gain characteristic diagram in the multi-core fiber of FIG.

FIG. 3 shows the core spacing in the multi-core fiber of FIG.
It is a bandwidth characteristic figure.

FIG. 4 shows a second embodiment of an Er-doped multicore fiber according to the present invention, (a) is a sectional view, (b) is AA ′, BB ′, and CC ′ in (a). Shows the refractive index distribution in each cross section.

5A and 5B show a third embodiment of an Er-doped multicore fiber according to the present invention, FIG. 5A is a sectional view, and FIG. 5B is a sectional view taken along line AA ′, BB ′, and CC ′ in FIG. Shows the refractive index distribution in each cross section.

6A and 6B show a fourth embodiment of an Er-doped multicore fiber according to the present invention, wherein FIG. 6A is a sectional view and FIG. 6B is a sectional view taken along the line AA ′, BB ′, CC ′ in FIG. Shows the refractive index distribution in each cross section.

FIG. 7 is a distribution characteristic diagram showing an example of a distribution (stepwise distribution) of Er addition concentration in the core according to the present invention.

FIG. 8 is a distribution characteristic diagram showing another example of the distribution of the Er addition concentration in the core (gradual distribution in the radial direction) according to the present invention.

FIG. 9 is a connection diagram showing a first embodiment of an optical amplifier using an Er-doped multicore fiber according to the present invention.

FIG. 10 is a connection diagram showing a second embodiment of an optical amplifier using an Er-doped multicore fiber according to the present invention.

11 is a connection diagram showing a configuration example of an optical amplification and distribution device configured using the optical amplifier shown in FIG.

FIG. 12 is a connection diagram showing a configuration example of an optical amplification repeater configured using the optical amplifier shown in FIG.

FIG. 13 is a connection diagram showing another configuration example of the optical amplification repeater.

FIG. 14 is a core spacing d-power incident / exit characteristic diagram at a wavelength of 0.98 μm.

FIG. 15 is a characteristic diagram of core spacing d-power incidence / emission at a wavelength of 1.55 μm.

FIG. 16 is a cross-sectional view showing an example of a conventional Er-doped multicore fiber.

FIG. 17 is a connection diagram showing an optical amplifier using the Er-doped multicore fiber shown in FIG.

FIG. 18 is a wavelength-gain characteristic diagram in which the wavelength characteristic of gain in the Er-doped multicore fiber having the configuration of FIG. 17 is measured.

FIG. 19 is a characteristic diagram showing the relationship between the core spacing d of a multicore fiber and the 1 dB bandwidth of an optical amplifier.

[Explanation of symbols]

 1a, 1b, 1c, 1d, 1e, 1f Surrounding core 1g Center core 2 Primary clad layer 3 Secondary clad layer 4 Er-doped multi-core fiber 6a, 6b WDM circuit 8a, 8b Isolator 12a, 12b Pumping semiconductor laser 13a, 13b Pumping light 14 Optical star coupler 16a, 16b, 16c Dispersion shift fiber 17a, 17b Optical amplifier 18a, 18b Optical multiplexing / demultiplexing circuit 21 Dispersion compensation device 100 Intermediate layer

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01S 3/07 H01S 3/07 3/17 3/17

Claims (19)

[Claims] 1. A multi-core fiber comprising a plurality of rare earth element-doped cores covered with a cladding layer having a predetermined refractive index, wherein the plurality of cores are arranged at the center of the plurality of cores. A first core having a first index of refraction greater than the predetermined index of refraction, and a second index of refraction disposed outside the first core and greater than the first index of refraction. A multi-core fiber comprising a second core. 2. The first and second cores are added with Al in addition to the rare earth element, and the cladding layer includes a primary cladding layer that covers the first and second cores, and The multi-core fiber according to claim 1, wherein the multi-core fiber is composed of a secondary clad layer provided on the outside. 3. The multi-core fiber according to claim 2, wherein the primary cladding layer has a smaller refractive index than the secondary cladding layer. 4. The first and second cores are made of SiO 2.
_TwoGlass, SiO _Two-GeO_TwoGlass or S
iO_Two-GeO_Two−P_TwoO_FiveAt least Al in the system glass
Is 5000ppm, and Er is at least 200ppm
The mulch according to claim 2, which is added.
Core fiber. 5. A multi-core fiber configured by coating a plurality of cores to which a rare earth element is added with a cladding layer, wherein the plurality of cores include a first core disposed in a central portion of the plurality of cores. A multi-core fiber, which is arranged outside the first core and includes a second core containing a rare earth element in an amount larger than the amount of the rare earth element added to the first core. 6. The multi-core fiber according to claim 5, wherein the rare earth element is added to the first core and the second core so that the rare earth element is radially distributed in each core. 7. The multi-core fiber according to claim 5, wherein the first core has a refractive index higher than that of the cladding layer and lower than that of the second core. 8. The first and second cores are doped with Al in addition to the rare earth element, and the cladding layer includes a primary cladding layer that covers the first and second cores, and The multi-core fiber according to claim 5, wherein the multi-core fiber is composed of a secondary clad layer provided outside. 9. The multi-core fiber according to claim 5, wherein the primary cladding layer has a smaller refractive index than the secondary cladding layer. 10. The first and second cores are made of SiO ₂
Glass, SiO ₂ —GeO ₂ glass, or Si
The multi-core fiber according to claim 5, wherein Al is added at least 5000 ppm and Er is added at least 200 ppm to the O ₂ —GeO ₂ —P ₂ O ₅ based glass. 11. A plurality of cores to which a rare earth element is added are coated with a cladding layer having a predetermined refractive index,
The plurality of cores are arranged in the central portions of the plurality of cores, and are arranged outside the first core and a first core having a first refractive index higher than the predetermined refractive index, and A multi-core fiber composed of a second core having a second refractive index higher than the first refractive index; a WDM circuit provided on the input side, output side, or both sides of the multi-core fiber; and the WDM circuit. An optical amplifier using a multi-core fiber, comprising: a pumping light source for supplying pumping light to an optical fiber; and an isolator provided between the WDM circuit and an input end or an output end. 12. A structure in which a plurality of cores to which a rare earth element is added are covered with a clad layer having a predetermined refractive index,
The plurality of cores, a first core arranged in the central portion of the plurality of cores, and arranged outside the first core,
A multicore fiber composed of a second core containing a rare earth element in an amount larger than the amount of the rare earth element added to the first core; and a WDM circuit provided on the input side, output side, or both sides of the multicore fiber. An optical amplifier using a multi-core fiber, comprising: a pumping light source for supplying pumping light to the WDM circuit; and an isolator provided between the WDM circuit and an input end or an output end. . 13. The excitation light has a wavelength of 0.98 μm band or 1.48 μm band.
An optical amplifier using the multi-core fiber according to 1 or 12. 14. A structure in which a plurality of cores to which a rare earth element is added are covered with a clad layer having a predetermined refractive index,
The plurality of cores are arranged in the central portions of the plurality of cores, and are arranged outside the first core and a first core having a first refractive index higher than the predetermined refractive index, and A multi-core fiber composed of a second core having a second refractive index higher than the first refractive index; a WDM circuit provided on the input side, output side, or both sides of the multi-core fiber; and the WDM circuit. A pumping light source for supplying pumping light to, an isolator provided between the WDM circuit and an input end or an output end, an input side, an output side of an optical amplifier of the multicore fiber,
Alternatively, an optical amplification repeater using a multi-core fiber, characterized in that it comprises a dispersion shift fiber connected to both sides. 15. A plurality of cores to which a rare earth element is added are coated with a cladding layer having a predetermined refractive index,
The plurality of cores, a first core arranged in the central portion of the plurality of cores, and arranged outside the first core,
A multicore fiber composed of a second core containing a rare earth element in an amount larger than the amount of the rare earth element added to the first core; and a WDM circuit provided on the input side, output side, or both sides of the multicore fiber. An excitation light source for supplying excitation light to the WDM circuit, an isolator provided between the WDM circuit and an input end or an output end, an input side, an output side of an optical amplifier of the multicore fiber,
Alternatively, an optical amplification repeater using a multi-core fiber, characterized in that it comprises a dispersion shift fiber connected to both sides. 16. The optical amplification repeater using a multi-core fiber according to claim 14, wherein a dispersion compensation device is connected to the dispersion shift fiber in the middle thereof. 17. An optical multiplexer / demultiplexer circuit is provided on the input side, output side, or both sides of the device.
Alternatively, an optical amplification repeater using the multicore fiber according to item 16. 18. A plurality of cores to which a rare earth element is added are coated with a cladding layer having a predetermined refractive index,
The plurality of cores are arranged in the central portions of the plurality of cores, and are arranged outside the first core and a first core having a first refractive index higher than the predetermined refractive index, and A multi-core fiber composed of a second core having a second refractive index higher than the first refractive index, and W provided on the input side, output side, or both sides of the multi-core fiber
A DM circuit, a pumping light source for supplying pumping light to the WDM circuit, an optical amplifier including an isolator provided between the WDM circuit and an input end or an output end, and an output side of the optical amplifier And an optical star coupler which distributes and outputs the amplified optical signal output from the optical amplifier to a plurality of different wavelengths, and an optical amplification and distribution device using a multi-core fiber. 19. A structure in which a plurality of cores to which a rare earth element is added are covered with a clad layer having a predetermined refractive index,
The plurality of cores, a first core arranged in the central portion of the plurality of cores, and arranged outside the first core,
A multi-core fiber composed of a second core containing a rare earth element in an amount larger than the amount of the rare earth element added to the first core; and a WDM circuit provided on the input side, output side, or both sides of the multi-core fiber. A pumping light source for supplying pumping light to the WDM circuit, an optical amplifier including an isolator provided between the WDM circuit and an input end or an output end, and an output side of the optical amplifier. And an optical star coupler for distributing and outputting the amplified optical signal output from the optical amplifier to a plurality of different wavelengths, an optical amplifying and distributing apparatus using a multi-core fiber.